Purification of succinic acid



Patented Jan. 30, 1934 UNITED STATES PURIFICATION OF SUCCINIC ACID Johann A. Bertsch and Arthur H. Krause, St. Louis, Mo., assignors, by mesne assignments, to Monsanto Chemical Company, a corporation of Delaware N0 Drawing. Application May 2, 1930 Serial No. 449,347

8 Claims.

This invention relates to the manufacture of succinic acid and succinates from maleic or fumaric acids and salts.

succinic acid and succinates can be made by reducing the corresponding maleic or fumaric composition, preferably the former, by hydrogenation, by means of reducing agents such as zinc or electrolytically.

Inasmuch as the product is employed in the I manufacture of pharmaceuticals a high standard of quality is demanded. Among other requirements, in order to comply with these standards, the product must have less than 0.05 percent ash and 1 g. succinic acid shall not decolorize more than 0.2 cc 0.1 normal permanganate solution for decolorizing.

In general the reduction of maleic acid to succinic acid proceeds smoothly and efiiciently until only a small fraction of maleic acid remains.

Y The reduction of the last few percent, however, is

wasteful and can be efiected only with difficulty. Thus, for example, in the electrolytic reduction of maleic acid one obtains a 97% reduction in a-comparatively short period of time and with a relatively high current efficiency. However, in order to efiect quantitative conversion the time and amount of current necessary adds greatly to the cost of the product.

One of the principle objects of this invention is to provide a method of manufacturing succinic acid according to which crude succinic acid or succinates are first formed, after which they are separated from their corresponding unsaturated starting materials to form a product which is remarkably pure.

A further object of the invention is to provide a simple and convenient method of preparing a succinic acid product which is low in ash content and which requires only one drop 0.1 normal permanganate to produce a pink coloration that persists for 30 seconds at C.

According to this invention one reduces fumaric or maleic acid in the usual manner until only a few percent of the unreacted raw material remains which ordinarily would be diflicult to remove. Thereafter the solution is treated with an oxidizing agent such as permanganate which reacts with the maleic and fumaric acids and which can thereafter be easily separated from the succinic acid.

We have found that if a solution of potassium permanganate is added to a solution of the crude succinic acid or salt with or without mineral acid the maleic acid is destroyed and the unreacted permanganate and manganese dioxide may be absorbed from the solution by means of charcoal. After filtering the succinic acid or salt solution, the product is isolated from its solution and will be found to have a very low ash content and practically no permanganate. 60

A crude succinic acid or salt containing the maleic acid and analogous impurities may be obtained from any convenient source. One such source is that obtained by the electrolytic reduction. According to this invention a concentrated solution of crude succinic acid or salt is first tested for the purpose of ascertaining the quantity of permanganate required. To this end a small sample of thesolution is mixed with sulphuricacid and titrated with a standardized solu-' tion of permanganate inthe usual manner. I

Inasmuch as the amount of ash obtained in the. final product is substantially less when thepermanganate treatment is effected in solution free from mineral acid and since the-manganese is reduced in a solution free from mineral acid from a valence of '7 to a valence of l, whereas mineral acid solution it is reduced fromfa valence of 7 to a valence of 2, the amount of permanganate consumed according to the titrationin presence 80. of mineral acid must be increased by five-thirds in order that a sufficient amount of the oxidizing agent will be employed when used in absence of mineral acids. g

A concentrated aqueous solution of the calculated amount of permanganate is then added to the solution of crude succinic acid and the mixture maintained at. about C. for approximately one half hour, preferably while agitating the same. Manganese dioxide is precipitated which can be filtered without difficulty. After a half hour the solution should evidence at least a slightly pink coloration, indicating the presence of free potassium permanganate. A quantity of charcoal is then added to the mixture which absorbs or decolorizes the excess permanganate and colloidal M1102. Subsequently the solution is filtered, evaporated, cooled and the product crystallized, which will be found to contain less than 0.05 percent ash and will not decolorize a solution of permanganate. In addition to removing maleic and furnaric impurities the above described process removes color contaminating substances such as quinone condensation products that are associated frequently with maleic acid and will also remove impurities which impart undesirable odors to the product.

When a succinic acid solution contains relatively large amounts of inorganic impurities such as metal salts, particularly those of iron, one obtains a purer crystalline product if after filtering the oxidized solution, there is added thereto a small amount of mineral acid such as hydrochloric. The resulting refined succinic acid will be found to be substantially free of the inorganic salt impurities.

If desired one may oxidize the maleic acid with an alkali permanganate in a mineral acid solution; however, the amount of ash in the final product is usually increased to approximately 0.1 percent. Where, however, this quantity is not objectionable the results Will be found to be equally satisfactory. Moreover the permanganate is consumed more efficiently in an acid medium.

It will be understood, of course, that other oxidizing agents of the permanganate class such as sodium permanganate, may be employed and other conditions for the oxidation may be selected. Similarly, materials other than charcoal may be employed as absorbing agents. These may include fullers earth, bone char, etc. Thus, although we have described but a single example of the principles of our invention and have indicated certain modifications it will be apparent to those skilled in the art that the invention is not so limited but that it may be practiced in many other forms without departing from its spirit. Wherefore, we desire that it be restricted only as indicated by the appended claims.

What we claim is:

1. In the manufacture of a member of the group of compounds consisting of succinic acid and its salts, the steps which consist in hydrogenating the corresponding unsaturated composition, interrupting the hydrogenation before the reaction has proceeded to completion, decomposing the unreacted, unsaturated, organic composition by means of an oxidizing agent that is inert to the hydrogenated product and subsequently isolating the product.

2. In the manufacture of succinic acid by the hydrogenation of maleic acid, the steps which consist in interrupting the hydrogenation before A completion, treating the resulting crude succinic acid containing some unreacted maleic acid with an alkali metal permanganate and isolating the product.

3. In the manufacture of a member of a group 7 of compounds consisting of succinic acid and its of the unreacted raw material with a water soluble permanganate, filtering and thereafter crystallizing the product from the filtrate.

4. In the manufacture of a member of a group of compounds consisting of succinic acid and its salts by the hydrogenation of the corresponding unsaturated composition, the steps which consist in treating a mineral acid free solution of the hydrogenated mixture with a water soluble permanganate under conditions whereby manganese dioxide is formed thereby destroying the remaining unreacted organic compositions, mixing an absorptive agent therewith, filtering the mixture and isolating the product from the filtrate.

5. In the manufacture of a member of a group of compounds consisting of succinic acid and its salts by the hydrogenation of the corresponding unsaturated compound, the steps which comprise treating a partially hydrogenated water solution containing such composition with a water soluble permanganate to decompose the unreacted compounds, the acid concentration during the permanganate treatment being such that the manganese dioxide formed remains undissolved, mixing an absorptive agent therewith, separating the solid matter and isolating the product.

6. In the manufacture of succinic acid that step in the refining of the succinic acid whereby inorganic salt contamination of the crystallized product is reduced which consists in adding a small quantity of hydrochloric-acid to an aqueous solution of the succinic acid and thereafter crystallizing the succinic acid from such solution.

7. In the manufacture of a member of a group of compounds consisting of succinic acid and its salts by the reduction of the corresponding unsaturated composition, the steps which consist in interrupting the reduction before the completion of the reaction, treating the reduced mixture with an aqueous soluble permanganate thereby destroying the unreacted, unsaturated organic compositions, mixing the resulting treated mixfture with an agent capable of eliminating any excess permanganate, filtering the mixture and isolating the product in the filtrate.

8. The method as defined in claim '7 and further characterized in that the permanganate eliminating agent consists of a material selected from a group consisting of the following: charcoal, bone char and fullers earth.

JOHANN A. BERTSCI-I. ARTHUR H. KRAUSE. 

